US President Donald Trump spoke with his Afghan counterpart Ashraf Ghani and condemned the terror attack in Kabul, describing it as "barbaric".

At least 90 people were killed and hundreds wounded when a massive truck bomb ripped through Kabul's diplomatic quarter during rush hour, in the deadliest attack in the Afghan capital since 2001.

"He condemned the attack, which occurred during the holy month of Ramadan, underscoring the barbaric nature of the terrorists who are enemies of all civilised peoples," the White House said in a readout of the telephonic conversation between the two leaders.

Conveying condolences to the families and friends of those killed and injured in the blast, Trump commended the bravery of the first responders, who worked quickly to support the wounded.

"He also commended Afghan security forces for their steadfast efforts to defend their people from enemies who would seek to deny them the security and prosperity," the White House said.

According to the White House, the United States Embassy is working with Afghan and coalition partners to assist the victims and help the National Unity Government pursue those responsible for the attack.

Strongly condemning the deadly bombing, US Secretary of State Rex Tillerson offered his deepest condolences to the families and friends of those who were killed and injured.